Y2O3-MgO纳米复相红外透明陶瓷制备及其性能研究

以商用Y2O3、MgO纳米粉体为原料,通过球磨混合方法制备了不同Y2O3/MgO配比的Y2O3-MgO纳米复合粉体,使用X射线衍射、扫描电镜、能量色散谱等表征手段对制备粉体的晶体结构、形貌、成分以及均匀性进行了表征。然后采用热压烧结方法制备Y2O3-MgO复相红外透明陶瓷,使用红外光谱仪、维氏硬度计等测试设备对复相透明陶瓷的光学和力学性能进行了分析。重点研究了粉体配比、热压温度、保温和保压时间等关键制备参数对Y2O3-MgO复相红外透明陶瓷晶粒尺度、致密化程度、光学及力学性能的影响。并通过调控粉体制备工艺和热压烧结工艺,制备出了红外透过率达到~80%的Y2O3-MgO复相红外透明陶瓷。同时在Y2O3:Mg0=1:1时,该复相陶瓷的硬度达到了12.3 GPa。     

机械电子化在热压机上的应用

机械电子化技术的应用大大提高塑机行业的竞争能力。对传统热压机械电子化改造,提出了机械电子化设计方案、引入评价参数,形成具有特定功能和价值的高功能、高质量、高柔性、高可靠性和低耗能的产品     

Effect of size and shape of metal particles to improve hardness and electrical properties of carbon nanotube reinforced copper and copper alloy composites

Utilizing the extra-ordinary properties of carbon nanotube (CNT) in metal matrix composite (MMC) for macroscopic applications is still a big challenge for science and technology. Very few successful attempts have been made for commercial applications due to the difficulties incorporating CNTs in metals with up-scalable processes. CNT reinforced copper and copper alloy (bronze) composites have been fabricated by well-established hot-press sintering method of powder metallurgy. The parameters of CNT–metal powder mixing and hot-press sintering have been optimized and the matrix materials of the mixed powders and composites have been evaluated. However, the effect of shape and size of metal particles as well as selection of carbon nanotubes has significant influence on the mechanical and electrical properties of the composites. The hardness of copper matrix composite has improved up to 47% compared to that of pure copper, while the electrical conductivity of bronze composite has improved up to 20% compared to that of the pure alloy. Thus carbon nanotube can improve the mechanical properties of highly-conductive low-strength copper metals, whereas in low-conductivity high-strength copper alloys the electrical conductivity can be improved.     

硬纸筒专机的设计

介绍了硬纸筒加工热压机的设计方法,其中对结构强度的计算和了重点介绍。     

Rapid and low-cost carbon/carbon composites by using graphite slurry impregnated prepregs

A rapid and low-cost carbon/carbon (C/C) composites preparation method is proposed: graphite prepreg-coated carbon fiber fabric (CFF) is formed by hot pressing, followed by hot isostatic pressing and high temperature graphitization, to prepare C/C composite with low porosity and high crystallinity. In this method, the carbon fiber (CF) mass fraction can be precisely regulated in the range of 40–95% by the impregnation process conditions of CFF in graphite prepreg. The graphite particles in the preform were graphitized and bonded with CFF by high temperature graphitization. Finally, a ZrO₂ anti-ablative layer was applied using sol-gel method. The results show that when the CF mass fraction is 50%, the C/C composite with a crystallinity of 92.21 and a porosity of 3.47% can be obtained, with mass ablation rate of 0.23 mg/s and density of 1.62 g/m³. The method can prepare C/C composites with uniform density and high ablation resistance.     

Thermomechanical stability and inelastic energy dissipation as durability criteria for fuel cell gas diffusion media with pre-assembly effects

In this article, pre-assembly hot-press pressure and thermal expansion effects in gas-diffusion layers (GDLs) are addressed to explore the practicalities of the constitutive model reported in the companion article. A facile technique is proposed to include deformation history dependent residual strain effects. The model is implemented in the numerical environment and compared with widely followed conventional models such as isotropic and orthotropic material models. With the normal and accelerated thermal expansion effects no significant variation in stresses or strains is reported with the compressible GDL model in contrast to the conventional incompressible form of the GDL model. The present work identifies the critical differences with advanced and extended variants of the model along with conventional GDL material models in terms of planar stress/strain distribution and the membrane response. Finally, the model is simulated for micro-cyclic stress loads of varying amplitudes that imitate the real working conditions of fuel cell. The inelastic energy dissipation in GDLs is predicted using the proposed model, which is utilized further to distinguish the safe (elastic) and unsafe (inelastic shakedown) operating limits. The inelastic collapse of GDLs is shown to be a active function of high amplitude micro-cyclic load with high initial clamping load.     

UHMWPE彩色多孔薄板的加工技术

介绍了用冷压烧结成型法加工超高分子量聚乙烯(UHMWPE)彩色多孔薄板的技术。薄板外观呈紫色,规格为(厚×宽×长)1 5mm×120mm×500mm,平均孔径50μm～60μm,孔隙率达35%～40%。     

Role of synthesis method on microstructure and mechanical properties of graphene/carbon nanotube toughened Al2O3 nanocomposites

The effects of hot-pressing (HP) and spark plasma sintering (SPS) methods on the grain size, microstructural features, and mechanical behaviour of graphene nanoplatelet/carbon nanotubes (GNTs) reinforced Al₂O₃ nanocomposites were comprehensively studied. Different graphene nanoplatelet to carbon nanotube ratios were selected as the overall reinforcement content of composites prepared using HP and SPS. Highly densified samples (>98%) were obtained at 1650 °C under 40 MPa in Ar atmosphere, with dwell times of 1 h and 10 min for HP and SPS respectively. Both types of sample showed a mixture of inter- and transgranular fracture behaviour. A 50% grain size reduction was observed for samples prepared by HP compared to SPS samples. Both types of samples achieved a high flexural strength and fracture toughness of >400 MPa and 5.5 MPa m^1/2, whilst SPS samples peaked at relatively lower GNT contents than those for the HP samples. Based on analyses of the morphology, grain sizes and fracture mode, similar toughening mechanisms for both types of sample were observed, involving the complex characteristics of the combined GNT fillers.     

Fabrication and mechanical properties of Al2O3-Si3N4/ZrO2-Al2O3 laminated composites

In this paper, Al₂O₃-Si₃N₄/ZrO₂-Al₂O₃ laminated composites were fabricated by tape casting and hot press sintering, and the relationships between the process, microstructure, and mechanical properties of Al₂O₃-Si₃N₄/ZrO₂-Al₂O₃ laminated composites were determined. The SiAlON phase was found in the Al₂O₃-Si₃N₄ layer, and liquid-phase sintering was proposed. Nano-scratch tests were carried out to investigate the interface bonding strength of the laminates. The distribution of residual stresses, generated due to the different coefficients of thermal expansion between the different layers, was estimated according to lamination theory and confirmed using Vickers indentation. When the sintering temperature was 1550 °C, the sintered laminated ceramics had good mechanical properties, with a maximum strength and toughness of 413 MPa and 6.2 MPa m^1/2, respectively. The main toughness mechanics of laminated composites was residual stress.     

Effect of the starting AlN content on the phase formation and property of the novel in-situ fabricated X-SiAlON/BN composites

Novel in-situ X-SiAlON reinforced BN composites were first fabricated via the procedure of mechanical alloying plus hot press sintering. The effects of the starting AlN content (0∼25 vol%) on phase formation, evolution and microstructure were carefully investigated. XRD results indicated that AlN content was the crucial factor in the phase composition and evolution in the composites, for instance, excess AlN leading to the transformation from X-SiAlON to β-SiAlON. The relationships of AlN content with mechanical, thermal and dielectric properties of the composites were also involved in this study. The composite with the 15 vol% AlN, mainly consisting of X-SiAlON and BN, exhibited the best mechanical properties (flexural and fracture strength were 337.5 MPa and 4.15 MPa.m^1/2, respectively), low thermal conductivity as well as the excellent dielectric properties (ε < 5.71), which enabled it to be a promising candidate for the application of high-temperature structural/ functional materials.